add role="tooltip" to tooltips by default to improve accessibility

Fix: IE10 or lower incorrectly determines the scrollheight of the body. ...

fix scrollspy for targets within tabs

See https://github.com/paypal/bootstrap-accessibility-plugin/blob/master/README.md#tooltip

upgrade to grunt-css-flip v0.2.0

comply with .dropdown-menu.pull-right deprecation in docs

Closes #13045

add role="alert" to Alert examples, to improve accessibility

Per https://github.com/paypal/bootstrap-accessibility-plugin/blob/d8fcbcd3fe86f0cb47fda0ffe269b2c7a2131f07/README.md#alert

Fixed typo at docs/examples/rtl/index.php

The filename generated at dist/css/ called 'bootstrap-rtl.min.css'.

Conflicts:
	dist/css/bootstrap.css.map
	docs/assets/js/customize.min.js
	docs/dist/css/bootstrap.css.map

Fixes #13003: Move padding on radio and checkbox options from the surrounding div to the label to remove the no-click deadzone caused by negative margin

Modular the mixins

Correct the page name

Note that while v1.4.3 is the latest stable version, it has a nasty Windows bug.
(https://github.com/jekyll/jekyll/issues/1948)

Add missing customizer comment

"Getting started" is used in the docs.

Conflicts:
	dist/css/bootstrap.css.map
	docs/assets/js/raw-files.min.js
	docs/dist/css/bootstrap.css.map

Use `outline: 0` consistently